Other than the use of “should”, the instruction is very clear that traditional custom includes a sanctuary (or “presence”) lamp. The same custom applies to both East and West.
IMHO, I imagine that “should” is used in the instruction precisely because of the presence of fire laws in some places as well the fact that “freedom of religion" is not the law everywhere and is not honored everywhere that it supposedly applies.”.
In spite of the “should,” the instruction is also clear as to what a sanctuary (or “presence”) lamp should be. I would venture here that the only way an electric light could substitute for oil or wax is if the local fire laws absolutely and absolutely forbid an unattended lamp. In which case, there is really no sanctuary (or “presence”) lamp anyway and we come back to what seems to me to be the reason for the subjunctive in the first place.